我現(xiàn)在在用AVAduioPlayer在后臺(tái)播放音效（白噪音軟件），然后應(yīng)用是允許用戶設(shè)置播放時(shí)間的，但是當(dāng)應(yīng)用在后臺(tái)時(shí)，NSTimer的回調(diào)函數(shù)是不會(huì)被調(diào)用的，這個(gè)時(shí)候我該如何停止音效呢？代碼：-(void)play:(NSString*)soundNamewithTime:(NSNumber*)time{NSURL*soundUrl=[NSURLfileURLWithPath:[NSStringstringWithFormat:@"%@/sounds/%@.m4a",[[NSBundlemainBundle]resourcePath],soundName]];_audioPlayer=[[AVAudioPlayeralloc]initWithContentsOfURL:soundUrlerror:nil];_audioPlayer.numberOfLoops=-1;[_audioPlayerplay];[[AVAudioSessionsharedInstance]setCategory:AVAudioSessionCategoryPlaybackerror:nil];[[AVAudioSessionsharedInstance]setActive:YESerror:nil];[selfscheduleStopSound:time];//howtoimplementit.}